1. Field of the Invention
The present invention relates to pigment compositions which have excellent properties for various applications, particularly with regard to non-flocculation and non-crystallization, and to use of such pigment compositions.
2. The Prior Art
In general, useful pigments which exhibit clear colour tone and high tinting strength in various coating compositions consist of fine particles. However, when fine particles of pigment are dispersed in non-aqueous vehicles such as offset printing inks, gravure printing inks and paints, it is difficult to obtain stable dispersions and various problems arise which have a serious influence on the preparation, and also on the value, of the resulting product. For instance dispersions which contain pigments consisting of fine particles are often highly viscous and thus not only is it difficult to withdraw the dispersion product from a dispersing machine and transport it but also, in a worse case, it cannot be used due to gellation during storage. Further, when pigments of different types are mixed, undesirable phenomena such as colour separation by flocculation and precipitation can take place and may cause the dispersion system to be uneven in colour and may also considerably lower the tinting strength. There may also arise problems such as lowering of gloss, an inferiority of levelling and the like in films made from the dispersion system.
In addition to the problem of dispersion of the pigment, some organic pigments undergo a phenomenon involving a change in the crystal structure of the pigment. That is, crystal particles of a pigment which are unstable (from an energy viewpoint) change their sizes and form into a more stable state in a non-aqueous vehicle such as is used for offset printing ink, gravure printing ink and paint and may thus damage the commercial value of the dispersion system, due to a remarkable change in colour tone, reduction of tinting strength and formation of coarse particles.
In order to improve the anti-flocculation and crystal stability of pigments as mentioned above, heretofore there have been proposed a number of pigments including copper phthalocyanine pigments and quinacridone pigments.
The prior attempts may be broadly classified from a technical point of view into the following categories. One approach includes coating the surfaces of pigment particles with colourless compounds such as silicon oxide, aluminum oxide and tert-butyl benzoate as disclosed in U.S. Pat. Nos. 3,370,971 and 2,965,511. The second class includes, as typically described in Japanese Patent Publication No. 41-2466, U.S. Pat. Nos. 4,088,507 and 2,761,865, processes of admixing pigments with compounds which are obtained by introducing onto the organic pigment, as a matrix skeleton, substituents (on side chains) such as a sulphonyl group, a sulfonamide group, an aminomethyl group, a phthalimidemethyl group and the like.
The processes of the second class are better than those of the first class in that the second class of processes provide better non-flocculation and crystal stability and ensure easy preparation of pigment compositions.
However, the second class of processes have a disadvantage, in that, because the added compound is derived from a compound of the same chemical structure as an intended pigment and thus possesses an inherent intense colour, its application is severely restricted when such a compound is used in combination with a pigment whose tone colour is different from the compound. Accordingly, compounds corresponding to individual pigments must be provided, which is very disadvantageous in preparing pigment compositions.
In order to overcome the above disadvantage of the second class of processes, there has been proposed (in Japanese Laid-open Publication No. 54-17932) a pigment composition, as a third class, in which colourless or slightly coloured aromatic compounds, which are obtained by incorporating aliphatic hydrocarbon chains having more than 5 atoms into aromatic compounds having at least 9 atoms which constitute a ring, are added to pigments. However, investigations made by the present inventors have revealed that this pigment composition did not show a satisfactory effect when non-aqueous vehicles, and particularly aromatic solvents such as xylene, toluene and the like, are used.
The inventors of the present invention have made an intensive study of methodologies to inhibit flocculation and to improve the crystal stability of pigments. As a result, it has been found that substantially colourless aromatic compounds which have a substituent of a specific type are effective for the intended purpose when used in combination with pigments.
According to the present invention, there is provided a pigment composition comprising 100 parts by weight of a pigment and from 0.3 to 30 parts by weight of a colourless or slightly coloured aromatic compound having the following general formula (I) ##STR4## wherein Q represents a residue of an aromatic polycyclic compound which is joined directly or through A to --SO.sub.2 --, A represents a member selected from the group consisting of --O--, ##STR5## --S--, --CO--, --SO.sub.2 --, ##STR6## a divalent phenylene residue or a combination thereof, in which R.sub.4 and R.sub.5 represent, independently, a hydrogen atom or an alkyl group containing from 1 to 4 carbon atoms, R.sub.1 and R.sub.2 represent, independently, a hydrogen atom or an alkyl group containing from 1 to 4 carbon atoms, or together form a heterocyclic ring together with N* in the formula (I), R.sub.3 represents a hydrogen atom or an alkyl group containing from 1 to 20 carbon atoms, m is a integer of from 1 to 6 and n is an integer of from 1 to 3.
The residues of the aromatic polycyclic compounds represented by Q in the general formula (I) include, for example, those of naphthalene, anthracene, phenanthrene, pyrene, chrysene, indole, thiazole, benzimidazole, quinoline, acridone, anthraquinone, phenothiazine, quinazoline, carbazole, benzanthrone and perylene. Q may also include other substituents such as --R.sub.6, --OR.sub.6, ##STR7## --COOR.sub.6, --NHCOR.sub.6, ##STR8## --NR.sub.6 --CO--R.sub.7, --NO.sub.2, --CN, --CF.sub.3 and --SO.sub.3 M, in which R.sub.6 and R.sub.7 represent, independently, a hydrogen atom, a saturated or unsaturated alkyl group containing from 1 to 20 carbon atoms or an aryl group and M represents one equivalent of a mono- to trivalent cation.
A of the general formula (I) represents such divalent groups as defined hereinabove or a combination thereof, but Q may be bonded to --SO.sub.2 -- radical of the compound (I) directly, not through A. Combined divalent groups may be combinations of three or more groups such as ##STR9##
The preparation of the compounds represented by the general formula (I) is not specifically limited. For instance, some of the compounds may be easily obtained by reacting compounds of the following general formula (II) with compounds of the following general formula (III): ##STR10## (in which Q, A, R.sub.1, R.sub.2, R.sub.3, m and n have the same meanings as defined in the formula (I), and X represents a halogen atom).
The compounds of the general formula (I) have a basic group and thus show a strong affinity for the anionic moiety, for example a carboxyl group, of the resin component ordinarily contained in vehicles, which is a reason why the compound improves the dispersability of pigment in many applications.
Examples of pigment useful in the present invention include organic pigments, such as insoluble azo pigments, condensation azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolenone pigments, perylene pigments, perynone pigments, dioxazine pigments, lake pigments, vat dye pigments and basic dye pigments, and inorganic pigments such as carbon black, titanium oxide, chrome yellow, cadmium yellow, cadmium red, red iron oxide, iron black, zinc flower, Prussian blue and ultramarine.
The compounds of the general formula (I) used in the present invention are preferred to be used in an amount in the range of from 0.5 to 30 parts by weight per 100 parts by weight of the pigment. Amounts less than 0.5 parts by weight may not satisfactorily attain the aforementioned advantages, whereas amounts larger than 30 parts by weight may be usable but no increased effect can be expected.
Although the pigment composition according to the present invention may be prepared by merely mixing a powder of a pigment with a powder of the compound represented by the general formula (I), good results can also be obtained by mechanically mixing them in kneaders, rollers, attritor, super mills or various types of powdering or milling machines, by adding a solution containing the compound of the general formula (I) to a suspension system of a pigment in water or an organic solvent, thereby permitting the compound of the general formula (I) to deposit on the surface of the pigment, or by dissolving both an organic pigment and the compound of the general formula (I) in a solvent having strong dissolving power, such as sulphuric acid, and then co-precipitating them with use of a poor solvent, such as water.
When the thus-obtained pigment composition is used as a colourant for polyolefins, polyesters and various vinyl resins and as offset printing ink vehicles, such as for various resin-modified resins, and is used to prepare gravure printing inks, such as with lime rosin varnishes, polyamide resin varnishes and vinyl chloride resin varnishes, or is used to prepare nitrocellulose lacquers, room temperature drying or baking paints, urethane resin paints and the like, it serves to lower the viscosity of the dispersant and reduce the structural viscosity of the dispersion system and thus shows good fluidity as compared with a pigment used alone. In addition, the pigment composition according to the invention normally presents no problems such as colour separation or changes in crystalinity and imparts good colour tone and gloss to printed matter, mouldings or films.